As a new-generation unit with the most powerful functions and advanced performance, the Unified Power Flow Controller (UPFC) is the most commonly used Flexible AC Transmission (FACTS) unit so far. Integrated with various flexible control methods of FACTS elements, the unit can realize voltage regulation, series compensation, phase shift and other functions respectively or simultaneously simply by changing control laws. In addition, the UPFC unit can effectively control the distribution of power flow on the control circuit, improving the stability of power system.
However, as the HVDC project continues to grow in China, the number of DC converter stations is skyrocketing in the existing power grid. When the number of transformers and shunt converter is decreased at the parallel side of the Unified Power Flow Controller the problem to be solved is how to utilize the AC side of HVDC converter station to provide active power for the Unified Power Flow Controller, reduce operation costs and ensure reliable operation of power grid.